1. Field of the Invention
The present invention relates to magnetic disk drive systems, and more particularly to magnetic disk drive systems in which read/write locations on a rotating magnetic disk are identified by dividing a plurality of tracks on the disk into different concentric zones and establishing a succession of sectors along each track with sector length being different in the different zones.
2. Description of Related Art
It is well known in the field of magnetic disk drives to identify desired locations on one or more magnetic disks by dividing the tracks on the disk into a plurality of different concentric zones. Each track is also divided into a succession of sectors of equal length. The size (arcuate extent) of the sectors within each zone is different from the sizes of the sectors in the other zones. This is because, for a given recording density along the tracks of the magnetic disk, a data field of standard length requires a larger sector for tracks closer to the center of the disk than in the case of tracks further away from the disk center and closer to the outer edge thereof. Thus, the standard length field in a track relatively close to the center of a disk may require a sector which is as much as two times the size of the sector required by the same field recorded at the same density but in a track close to the outer edge of the magnetic disk. For this reason, it is common to define sectors which increase in arcuate size from the outermost track to the innermost track on the disk so as to obtain a generally uniform linear length for each sector and thereby achieve maximum recording density. For convenience, the disk is typically divided into a plurality of zones, with the tracks lying in each zone having a given sector size different from the sector size in the other zones. This is commonly referred to as constant density recording.
Various different schemes are used to identify the sectors within the tracks as the transducer is caused to address different tracks in response to track seek commands. One common technique uses timing signals generated in response to rotation of the magnetic disk as a reference to define the rotational position of the disk at any given instant. Servo burst signals or other track following signals recorded within the tracks of a dedicated servo disk, for example, are used to generate sync pulses as the disk rotates. The generation of such pulses in conjunction with an index pulse generated at the start of each revolution provides timing signals useful in determinating rotational position as the disk rotates. This information, in turn, is used to generate pulses which identify the sectors of a selected track when combined with a determination of the zone in which the track is located. The zone of the selected track is typically determined by sensing small fields of information recorded within the servo tracks which identify or define the zone in which the track is located. This information together with the timing signals provided in response to rotation of the magnetic disk enables the determination of sector location within the various tracks.
The arrangements just described are not without their disadvantages. Each different zone typically requires a different timing circuit in order to identify the sectors within such zone in response to the timing information. Such timing circuit may, for example, include a counter for counting the sync pulses generated by rotation of the disk. The counter counts down by a predetermined count before generating a sector pulse, following which the process is repeated. This is because the number of sync pulses generated in correspondence to each sector is fixed for each particular zone. Because a different counter and associated circuitry are required for each zone, the hardware requirements for the disk drive may be substantial. This is particularly true in cases where a relatively large number of zones are used in order to maximize use of the recording surface of the disk. In such instances, the space and cost requirements can be quite substantial.
A further problem arises in such disk drive systems due to the fact that the zones are typically preselected with the system thereafter being designed and built in a somewhat permanent fashion. For example, a system using disks of given size and recording density capability for a particular type of operation may dictate the establishment of a predetermined number of zones encompassing selected groups of tracks on the disk. The system is then built on this basis with the counting circuitry being hard-wired in accordance with the preselected zones. The system thereafter requires such zone pattern, and is not easily changed.
Typically, once the zones are established in such magnetic disk systems, a small field which identifies the zone is then periodically recorded on each servo track. During use, the magnetic transducer reads the identifying data when addressing a particular track so that the zone in which the track is located is identified. Because of this, considerable time and effort are required to record the tracks on the servo disk. Should it be desired to change the number of zones or the zone configuration on the disk or disks of the system, considerable effort is required to re-record the servo information.
A still further problem resides in the operations necessary to respond to each new track seek command. The timing circuitry for generating the sector pulses, for example, may require that the system await the next index pulse so that the circuitry can be properly synchronized. Relocation of the magnetic transducer to another track and sector, particularly within a different zone, may be complicated in other respects as well.
It would therefore be desirable to provide an improved magnetic disk drive system. Such an improved disk drive system should desirably be capable of implementing a multi-zone disk layout without the need for space consuming and costly hardware, particularly in instances where a relatively large number of zones are used. It would also be desirable to be able to vary the number and layout of the zones within a given system without making hardware changes. It would furthermore be desirable to eliminate the need for recording zone identifying information within the servo tracks. This would make the recording of the servo tracks relatively easy, both initially and upon changing the zone configuration within an existing design.